Conventionally, as a chain connection link connecting a chain or the like formed by connecting together elliptical annular links, there has been known a chain connection link in which a connection arm portion and a connection groove-shaped arm portion are respectively provided at one and the other of both arms of each of a pair of U-shaped links (PTL 1 and PTL 2). In this chain connection link, the connection arm portion of one U-shaped link is fitted into the groove portion of the connection groove-shaped arm portion of the other U-shaped link, and a connection shaft is inserted into through-holes provided in both arm portions, whereby the pair of U-shaped links are connected together in an annular form.
More specifically, in the chain connection link disclosed in PTL 1, a spring collar of a slightly larger outer diameter than the diameter of the shaft holes provided in the arms of the U-shaped links is fitted onto a small-diameter portion provided in the intermediate portion of the connection shaft. By providing a gap between the inner surface of the spring collar and the small-diameter portion, it is possible, in the chain connection link disclosed in PTL 1, to attach the spring collar through an easy operation.
In the chain connection link disclosed in PTL 2, the sectional configuration of a detachment prevention ring fixed to the intermediate portion of the connection shaft is elliptical; and the length of the minor axis thereof is smaller than the outer diameter of the connection shaft, and length of the major axis thereof is larger than the outer diameter of the connection shaft. Thus, in a state in which high load is being applied to U-shaped rods, even if a twisting action is applied between the U-shaped rods, it is possible to suppress plastic deformation beyond the elasticity limit of the detachment prevention ring. As a result, in the chain connection link disclosed in PTL 2, it is possible to suppress inadvertent detachment of the connection shaft.
In this way, the techniques adopted in the chain connection links disclosed in PTL 1 and PTL 2 relate to an improvement of a spring collar and a detachment prevention ring, and there exists as yet no technique related to an improvement in terms of the strength of a chain connection link taking into account the environment of use thereof.